The present invention relates to a hydropneumatic suspension system for a vehicle.
A vehicular hydropneumatic suspension system is known in which auto-levelling valves are built in hydropneumatic suspension units, respectively, one for each of wheel units of the vehicle, for supplying hydraulic fluid to, or discharging from the suspension units so as to regulate the level of the vehicle body. Each of the auto-levelling valves will supply hydraulic fluid to the suspension unit to which it is connected if the vehicle body lowers due to an increase in load or will discharge hydraulic fluid from the suspension unit if the vehicle body rises due to a reduction in load so as to regulate the level of the vehicle body.
With this known hydropneumatic suspension system it is possible to lower the vehicle body from a certain level to a level low enough to facilitate ingress into or engress from the vehicle by discharging hydraulic fluid from the suspension units.
The problem encountered in this known hydropneumatic suspension system is in sluggish response of the system to the operator's demand to lower the vehicle body from the certain level. This attributes to the fact that during the discharging operation hydraulic fluid is discharged not only from a power chamber within a strut of each of the suspension units but also from a gas cushion connected to the cylinder, in particular, from a liquid chamber, separated from a gas chamber by a flexible membrane, connected to the power chamber. Since the amount of hydraulic fluid accummulated within each gas cushion for normal operation of the gas cushion is considerably large, it takes a long time for discharging hydraulic fluid from the suspension units until the vehicle body lowers to the desired level.